The present invention relates to a ball joint including a housing, a ball stud, and a bearing seat. The ball stud has a ball head portion integrally formed with a stud portion and the bearing seat slidably envelops the ball head portion of the ball stud. The ball stud and bearing seat combination is placed into an inner chamber of the housing through an opening. A lubricant introduced into the inner chamber of the housing permits the ball head portion to slide within the bearing seat.
Japanese Patent Laid-open No. 1995-269557 discloses an example of the type of ball joint described above.
The ball joint disclosed in Japanese Patent Laid-open No. 1995-269557 includes a bearing seat composed of material that is both elastic and rigid. A plurality of load receiving portions and indented portions are formed on the outer surface of the bearing seat that faces the inner chamber of the housing. The load receiving portions and the indented portions are formed alternately and adjacent with each other, and the load receiving portions contact the bottom portion of the inner chamber of the housing. The points of contact between the load receiving portions and the bottom portion of the housing are different radial distances from the center of the bearing seat. The indented portions are separated a given distance from the bottom portion of the housing.
The bearing seat also includes a sliding portion and a space portion formed on the inner cylindrical surface of the bearing seat. The sliding portion of the bearing seat contacts the ball head portion of the ball stud, while the space portion provides a clearance between the ball head portion and the bearing seat. Thus, the bearing seat slidably envelops the ball head portion of a ball stud placed in the bearing seat.
The bearing seat is placed in the inner chamber of the housing so that the load receiving portions of the bearing seat contact the bottom portion of the housing. The ball stud is placed in the bearing seat with the ball head portion abutting the sliding portion. The load receiving portions and sliding portions form indented and space portions between the housing and the ball head portion, respectively. A load applied to the ball joint causes the bearing seat to elastically deform due to the presence of the indented portions and the space portions. The elastic restoring force that results from the deformation creates a pushing energy on the ball head portion. The pushing energy and elasticity of the bearing seat allows the ball joint to provide friction compensation while absorbing dimensional tolerances of the components. The elastic deformation also helps to absorb a heavy load, thereby increasing the load withstanding capability and durability of the ball joint.
The conventional ball joint described in Japanese Patent Laid-open No. 1995-269557 has the entire surface of the bearing seat except for the space portion in close contact with the ball head portion. In this configuration, it is difficult for the lubricant to flow between the bearing seat and the ball head portion. For this reason, there is a demand for a configuration which enables the lubricant to efficiently spread over nearly the entire surface between the bearing seat and the ball head portion. The configuration should permit the ball head portion to slide more easily due to increased lubrication, while maintaining stable torque and friction compensation.
A space portion which occupies virtually the entire surface of the bearing seat is impractical. While such a configuration would permit a lubricant to spread over nearly the entire surface between the bearing seat and the ball head portion, the ball head portion would rattle within the bearing seat. Moreover, this arrangement would make frictional compensation and absorption of dimensional tolerances impossible.